Particle-in-Cell study of impurity production from RF sheaths in front of ICRH actuators

The radio-frequency plasma sheath formed in front of an Ion Cyclotron Resonance Heating (ICRH) antenna is responsible for significant ion acceleration and consequent material sputtering and impurity emission. In order to characterize the emission process, we performed a set of parametric simulations using two kinetic codes, the hPIC2 Particle-in-Cell and the RustBCA sputtering code. hPIC2 solved the time-dependent structure of the radio-frequency sheath, capturing both RF sheath rectification and the time modulation of the plasma potential. hPIC2 provided the time-dependent energy-angle distributions of the ions impacting on the surface, which were then fed as an input to the RustBCA sputtering code, in order to produce RF-phase-resolved distributions of sputtered impurities. From the analysis of the results we observed that the impurity emission is highly non-linear along the RF cycle, mainly because of the large non-linearities of the sputtering behavior as a function of energy and angle of the impacting ions. The effect on the time-integrated fluxes of magnetic field inclination, RF voltage, density, and plasma temperature is highlighted.